1. Field of the Invention
This invention relates to molds for producing preforms, which are then molded into plastic bottles and containers, such as for containing beverages and the like. More specifically, this invention relates to an improved mold design having a combination of hardened material components and high heat transfer material components.
2. Description of the Related Art
The use of plastic containers as a replacement for glass or metal containers in the packaging of beverages has become increasingly popular. The advantages of plastic packaging include lighter weight, decreased breakage as compared to glass, and potentially lower costs. The most common plastic used in making beverage containers today is PET. Virgin PET has been approved by the FDA for use in contact with foodstuffs. Containers made of PET are transparent, thin-walled, lightweight, and have the ability to maintain their shape by withstanding the force exerted on the walls of the container by pressurized contents, such as carbonated beverages. PET resins are also fairly inexpensive and easy to process.
Most PET bottles are made by a process that includes the blow-molding of plastic preforms, which have been made by processes including injection molding. In order to increase the through-put of an injection molding machine, and thereby decrease the cost of each individual preform, it is desirable to reduce the cycle time for each injection and cooling cycle. However, the injected preform must cool sufficiently to maintain its molded dimensions before it is removed from the injection mold. Therefore, it would be desirable to utilize high heat transfer materials to form the injection mold in order to rapidly cool the injected preform. However, such high heat transfer materials are generally prone to rapid wear when used in such an environment, where high clamping pressures are necessary to maintain the injection mold in a closed position during the injection of molten polymer into the mold cavity. As a result, the potential of such high heat transfer materials have not previously been fully realized in the injection molding of preforms.